Sodium Carbonate

Sodium Carbonate

The hydrated salt is also known as washing soda or salt soda while the anhydrous salt, Na₂CO₃ is called soda ash or soda.

Sodium carbonate occurs in many lake waters. It also occurs in the ashes of many marine plants.

Preparation

Na₂CO₃ can be made by neutralizing NaOH solution with CO₂.

2NaOH + CO₂ → Na₂CO₃ + H₂O

The solution upon concentrating and cooling deposits crystals of the decahydrate, Na₂CO₃.10H₂O.

Physical Properties

(i) Sodium carbonate is a white crystalline solid. It forms a variety of hydrates like Na₂CO₃.H₂O, Na₂CO₃.7H₂O, Na₂CO₃.10H₂O. The common washing soda is the decahydrate.

(ii) Sodium carbonate melts at 852.1°C.

Chemical Properties

(i) Action on water: Sodium carbonate dissolves in water giving alkaline solution due to the hydrolysis.

Na₂CO₃ 2Na⁺ + CO₃^2-

CO₃^2- + H₂O →  HCO^-₃+ OH−

or CO₃^2- + 2H₂O →  H₂CO₃ + 2OH−

(ii) Action on acids: Acids decompose sodium carbonate to give carbon dioxide.

Na₂CO₃ + 2HCl →  2NaCl + H₂O + CO₂

Na₂CO₃ + H₂SO₄ →  Na₂SO₄ + H₂O + CO₂

(iii) Action on salts of non−alkali metals: It precipitates carbonates of the non−alkali metals.

MgCl₂ + Na₂CO₃ →  MgCO₃ + 2NaCl

ZnSO₄ + Na₂CO₃ → ZnCO₃ + Na₂SO₄

MnCl₂ + Na2CO₃ →  MnCO₃ + 2NaCl

2AgNO₃ + Na2CO₃ →  Ag₂CO₃ + 2NaNO₃

(iv) Action on sulphur and sulphur dioxide: Aqueous sodium carbonate reacts with sulphur and sulphur dioxide to give sodium thiosulphate, Na2S2O3.

Na₂CO₃ + SO₂ →  Na₂SO₃ + CO₂

Na₂SO₃ + S →  Na₂S₂O₃

(v) Action on carbon dioxide: Aqueous sodium carbonate reacts with carbon dioxide to give sodium bicarbonate.

Na₂CO₃ + H₂O + CO₂ →  2NaHCO₃

(vi) Action on sand (SiO2): When sodium carbonate is fused with sand, water glass or sodium silicate is formed.

Na₂CO₃ + SiO₂ → Na₂SiO₃ + CO₂↑

Sodium silicate

(water glass)

Uses

Sodium carbonate is used:

(i) for the manufacture of glass.

(ii) for washing purposes (Laundry works)

(iii) for the manufacture of other sodium compounds like sodium hydroxide, borax and hypo etc.

(iv) domestically as a cleansing agent.

(v) in paper and paint industries.

(vi) for softening hard water.

(vii) It is a constituent of fusion mixture which is a mixture of Na₂CO₃ and K₂CO₃ in equivalent proportions. The fusion mixture is used for the detection of basic radicals of insoluble salts.